With vehicles in which a power-on upshifting is executed in an automatic transmission in accordance with a shift command, shift control devices for vehicular automatic transmissions have heretofore been known. The shift control devices control a timing at which a shifting output is initiated such that an engine rotation speed at inertia-phase start timing during, for instance, a full-throttle upshifting falls in a predetermined range. One example of such devices is disclosed in, for instance, Patent Publication 1, which discloses a structure in which the relationship between either one of a throttle opening, transmission input torque and a vehicle speed and an inertia-phase commencing time is preliminarily stored. A prime-mover rotation speed at the inertia-phase commencing timing is estimated based on the stored relationship and prime-mover acceleration upon which a shift point is corrected such that the estimated prime-mover rotation speed falls in a given range.
With such a device, in usual practice, given shift lines (in a shifting pattern) are used to obtain the maximum output during the upshifting mode with an accelerator-opening or a throttle opening being filly opened (at a value of 100%). The shifting pattern is determined such that an engine rotation speed lies at a high rotation speed within a range to cause the engine rotation speed not to fall in a predetermined red zone and a fuel cutoff range determined at a level above the red zone. At the same time, the shifting lines are altered depending on a load capacity of the vehicle such that the shifting output is initiated at an optimum timing.
Meanwhile, there is a vehicle that is arranged to execute the power-on upshifting of the automatic transmission in accordance with the shift point. With such a vehicle, in order for the engine rotation speed at the inertia-phase commencing timing during, for instance, the full-throttle upshifting mode to approach a predetermined target engine rotation speed without exceeding beyond the predetermined target engine rotation speed, the following are required. That is, a need arises not only for correcting the shift point depending on piece-to-piece variations of automatic transmissions as disclosed in Patent Publication 1 but also for correcting the shift point depending on a variation in vehicle acceleration.
Such devices are disclosed in, for instance Patent Publications 2 and 3. Patent Publication 2 discloses a technology in which the learning of the shifting is conducted for each predetermined segment of vehicle acceleration to allow a learned result for the corresponding segment of vehicle acceleration to be selected during the shifting for correcting the shift point. Further, Patent Publication 3 discloses a technology in which the learning for the shift point is conducted in a learning amount per unit acceleration to allow the learning amount per unit acceleration to be converted depending on vehicle acceleration by referring to a given formula to allow the shift point to be corrected based on such a result.
[Patent Publication 1] Japanese Patent Application Publication No. 2004-316845
[Patent Publication 2] Japanese Patent Application Publication No. 2003-28284
[Patent Publication 3] Japanese Patent Publication No. 7-109247